The syntax documentation for SELECT in SQL COMMANDS section is unclear in explaining how to use multiple window definitions. It's easy to read it and believe that multiple WINDOW keywords, one for each definition, are correct, which is not the case.
This is how we've chosen to document this kind of grammar and I don't see a compelling reason to revisit that decision on the basis of this report. I could consider some additional wording regarding "each clause keyword only ever appears once in a given (sub)query" though that seems almost self-evident as part of the learning of SQL. The fact that you write WINDOW and then a comma-separated listing of names plus definitions is how that syntax diagram is read, just like with WITH, FROM, and GROUP BY clauses in the same diagram.
